1. Field of the Invention
The present invention relates to an apparatus for forming stress corrosion cracks which occur in base metal or welded parts (which are homogeneous or heterogeneous) used in equipment such as reactor heads, steam generators or the like of nuclear power plants, and, more particularly, to an apparatus for forming stress corrosion cracks, in which stress corrosion cracks occurring in the equipment of nuclear power plants or apparatus industries during operation can be directly formed in a piping material actually used in nuclear power plants under environmental conditions similar to those of the nuclear power plants, thus predicting a crack propagation rate, thereby reducing actual risks of nuclear power plants or apparatus industries and effectively assuring nondestructive testing capability.
2. Description of the Related Art
As is well known to those skilled in the art, there is a need to construct an experimental apparatus which operates under environmental conditions similar to those existing actual conditions which generate stress corrosion cracks in nuclear power plants. However, in the case of stress corrosion cracks occurring in a primary system, such as a steam generator, a pressure vessel of a reactor or the like, there is a dangerous probability of emitting radioactivity due to the lack of domestic simulation techniques.
Thus, in order to ensure the safety of nuclear power plants and the reliability of NDT technologies, it is very important to realize techniques for producing natural cracks similar to actual defects occurring in nuclear power plants during operation.
To this end, an experimental apparatus able to simulate actual conditions for generating stress corrosion cracks in nuclear power plant structures must be constructed. If so, the reliability and safety of nuclear power plants may be improved and techniques for precisely diagnosing defects in the power plants occurring during their operation may be advanced.
In this way, when techniques for simulating stress corrosion cracks in a piping material actually used in nuclear power plants and for precisely diagnosing defects are ensured, inspection methods during the operation of the power plants may be developed and also data for safety regulation and repair criteria of nuclear power plant structures may be obtained.
With the goal of forming stress corrosion cracks in a specimen, the following testing method is mainly illustrated.
Specifically, a specimen is produced in the form of a C-ring or a U-band and is then loaded into an autoclave, after which appropriate tensile or compressive stress is applied thereto. In such a state, corrosion environmental conditions are set, and high-temperature high-pressure conditions are applied, thus forming crack.
However, the conventional method of forming stress corrosion cracks is disadvantageous because the resulting cracks are obtained not using a piping material actually used for equipment of nuclear power plants or apparatus industries but using a simulation specimen, they are considerably different from actual cracks, thus making it impossible to effectively assure nondestructive testing capability.